Instrumentation and methods for use in implanting a cervical disc replacement device

ABSTRACT

Instrumentation for implanting an intervertebral disc replacement device includes a retaining device comprising a threaded attachment member for threaded engagement with the at least one mounting screw hole in the flange of the intervertebral disc replacement device, and a head flange extending from the threaded attachment member, wherein a portion of the head flange is in part abuttingly received against a side of the flange of the intervertebral disc replacement device and another portion of the head flange is partially received over a portion of the bone screw to prevent the bone screw from backing out of the at least one bone screw hole when the retaining device is fully engaged with the intervertebral disc replacement device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation in part of U.S. patent applicationSer. No. 10/688,632 (filed Oct. 17, 2003) entitled “Instrumentation andMethods for Use in Implanting a Cervical Disc Replacement Device” (“the'632 application”), which is a continuation in part of U.S. patentapplication Ser. No. 10/382,702 (filed Mar. 6, 2003) entitled “CervicalDisc Replacement” (“the '702 application”), which '632 and '702applications are hereby incorporated by reference herein in theirentireties.

FIELD OF THE INVENTION

This invention relates generally to systems and methods for use in spinearthroplasty, and more specifically to instruments for inserting andremoving cervical disc replacement trials, and inserting and securingcervical disc replacement devices, and methods of use thereof.

BACKGROUND OF THE INVENTION

The structure of the intervertebral disc disposed between the cervicalbones in the human spine comprises a peripheral fibrous shroud (theannulus) which circumscribes a spheroid of flexibly deformable material(the nucleus). The nucleus comprises a hydrophilic, elastomericcartilaginous substance that cushions and supports the separationbetween the bones while also permitting articulation of the twovertebral bones relative to one another to the extent such articulationis allowed by the other soft tissue and bony structures surrounding thedisc. The additional bony structures that define pathways of motion invarious modes include the posterior joints (the facets) and the lateralintervertebral joints (the unco-vertebral joints). Soft tissuecomponents, such as ligaments and tendons, constrain the overallsegmental motion as well.

Traumatic, genetic, and long term wearing phenomena contribute to thedegeneration of the nucleus in the human spine. This degeneration ofthis critical disc material, from the hydrated, elastomeric materialthat supports the separation and flexibility of the vertebral bones, toa flattened and inflexible state, has profound effects on the mobility(instability and limited ranges of appropriate motion) of the segment,and can cause significant pain to the individual suffering from thecondition. Although the specific causes of pain in patients sufferingfrom degenerative disc disease of the cervical spine have not beendefinitively established, it has been recognized that pain may be theresult of neurological implications (nerve fibers being compressed)and/or the subsequent degeneration of the surrounding tissues (thearthritic degeneration of the facet joints) as a result of their beingoverloaded.

Traditionally, the treatment of choice for physicians caring forpatients who suffer from significant degeneration of the cervicalintervertebral disc is to remove some, or all, of the damaged disc. Ininstances in which a sufficient portion of the intervertebral discmaterial is removed, or in which much of the necessary spacing betweenthe vertebrae has been lost (significant subsidence), restoration of theintervertebral separation is required.

Unfortunately, until the advent of spine arthroplasty devices, the onlymethods known to surgeons to maintain the necessary disc heightnecessitated the immobilization of the segment. Immobilization isgenerally achieved by attaching metal plates to the anterior orposterior elements of the cervical spine, and the insertion of someosteoconductive material (autograft, allograft, or other porousmaterial) between the adjacent vertebrae of the segment. Thisimmobilization and insertion of osteoconductive material has beenutilized in pursuit of a fusion of the bones, which is a procedurecarried out on tens of thousands of pain suffering patients per year.

This sacrifice of mobility at the immobilized, or fused, segment,however, is not without consequences. It was traditionally held that thepatient's surrounding joint segments would accommodate any additionalarticulation demanded of them during normal motion by virtue of thefused segment's immobility. While this is true over the short-term(provided only one, or at most two, segments have been fused), theeffects of this increased range of articulation demanded of theseadjacent segments has recently become a concern. Specifically, anincrease in the frequency of returning patients who suffer fromdegeneration at adjacent levels has been reported.

Whether this increase in adjacent level deterioration is trulyassociated with rigid fusion, or if it is simply a matter of theindividual patient's predisposition to degeneration is unknown. Eitherway, however, it is clear that a progressive fusion of a long sequenceof vertebrae is undesirable from the perspective of the patient'squality of life as well as from the perspective of pushing a patient toundergo multiple operative procedures.

While spine arthroplasty has been developing in theory over the pastseveral decades, and has even seen a number of early attempts in thelumbar spine show promising results, it is only recently thatarthoplasty of the spine has become a truly realizable promise. Thefield of spine arthroplasty has several classes of devices. The mostpopular among these are: (a) the nucleus replacements, which arecharacterized by a flexible container filled with an elastomericmaterial that can mimic the healthy nucleus; and (b) the total discreplacements, which are designed with rigid endplates which house amechanical articulating structure that attempts to mimic and promote thehealthy segmental motion.

Among these solutions, the total disc replacements have begun to beregarded as the most probable long-term treatments for patients havingmoderate to severe lumbar disc degeneration. In the cervical spine, itis likely that these mechanical solutions will also become the treatmentof choice.

It is an object of the invention to provide instrumentation and methodsthat enable surgeons to more accurately, easily, and efficiently implantfusion or non-fusion cervical disc replacement devices. Other objects ofthe invention not explicitly stated will be set forth and will be moreclearly understood in conjunction with the descriptions of the preferredembodiments disclosed hereafter.

SUMMARY OF THE INVENTION

The preceding objects are achieved by the invention, which includescervical disc replacement trials, cervical disc replacement devices,cervical disc replacement device insertion instrumentation (including,e.g., an insertion plate with mounting screws, an insertion handle, andan insertion pusher), and cervical disc replacement device fixationinstrumentation (including, e.g., drill guides, drill bits,screwdrivers, bone screws, and retaining clips).

More particularly, the devices, instrumentation, and methods disclosedherein are intended for use in spine arthroplasty procedures, andspecifically for use with the devices, instrumentation, and methodsdescribed herein in conjunction with the devices, instrumentation, andmethods described herein and in the '702 application. However, it shouldbe understood that the devices, instrumentation, and methods describedherein are also suitable for use with other intervertebral discreplacement devices, instrumentation, and methods without departing fromthe scope of the invention.

For example, while the trials described herein are primarily intendedfor use in distracting an intervertebral space and/or determining theappropriate size of cervical disc replacement devices (e.g., describedherein and in the '702 application) to be implanted (or whether aparticular size can be implanted) into the distracted intervertebralspace, they can also be used for determining the appropriate size of anyother suitably configured orthopedic implant or trial to be implanted(or whether a particular size can be implanted) into the distractedintervertebral space. And, for example, while the insertioninstrumentation described herein is primarily intended for use inholding, inserting, and otherwise manipulating cervical disc replacementdevices (e.g., described herein and, in suitably configured embodiments,in the '702 application), it can also be used for manipulating any othersuitably configured orthopedic implant or trial. And, for example, whilethe fixation instrumentation described herein is primarily intended foruse in securing within the intervertebral space the cervical discreplacement devices (e.g., described herein and, in suitably configuredembodiments, in the '702 application), it can also be used with anyother suitably configured orthopedic implant or trial.

While the instrumentation described herein (e.g., the trials, insertioninstrumentation, and fixation instrumentation) will be discussed for usewith the cervical disc replacement device of FIGS. 1 a-3 f herein, suchdiscussions are merely by way of example and not intended to be limitingof their uses. Thus, it should be understood that the tools can be usedwith suitably configured embodiments of the cervical disc replacementdevices disclosed in the '702 application, or any other artificialintervertebral disc having (or being modifiable or modified to have)suitable features therefor. Moreover, it is anticipated that thefeatures of the cervical disc replacement device (e.g., the flanges,bone screw holes, and mounting holes) that are used by the toolsdiscussed herein to hold and/or manipulate these devices (some of suchfeatures, it should be noted, were first shown and disclosed in the '702application) can be applied, individually or collectively or in variouscombinations, to other trials, spacers, artificial intervertebral discs,or other orthopedic devices as stand-alone innovative features forenabling such trials, spacers, artificial intervertebral discs, or otherorthopedic devices to be more efficiently and more effectively heldand/or manipulated by the tools described herein or by other toolshaving suitable features. In addition, it should be understood that theinvention encompasses artificial intervertebral discs, spacers, trials,and/or other orthopedic devices, that have one or more of the featuresdisclosed herein, in any combination, and that the invention istherefore not limited to artificial intervertebral discs, spacers,trials, and/or other orthopedic devices having all of the featuressimultaneously.

The cervical disc replacement device of FIGS. 1 a-3 f is an alternateembodiment of the cervical disc replacement device of the '702application. The illustrated alternate embodiment of the cervical discreplacement device is identical in structure to the cervical discreplacement device in the '702 application, with the exception that thevertebral bone attachment flanges are configured differently, such thatthey are suitable for engagement by the instrumentation describedherein.

More particularly, in this alternate embodiment, the flange of the upperelement extends upwardly from the anterior edge of the upper element,and has a lateral curvature that approximates the curvature of theanterior periphery of the upper vertebral body against which it is to besecured. The attachment flange is provided with a flat recess, centeredon the midline, that accommodates a clip of the present invention. Theattachment flange is further provided with two bone screw holessymmetrically disposed on either side of the midline. The holes havelongitudinal axes directed along preferred bone screw driving lines.Centrally between the bone screw holes, a mounting screw hole isprovided for attaching the upper element to an insertion plate of thepresent invention for implantation. The lower element is similarlyconfigured with a similar oppositely extending flange.

Once the surgeon has prepared the intervertebral space, the surgeon mayuse one or more cervical disc replacement trials of the presentinvention to distract the intervertebral space and determine theappropriate size of a cervical disc replacement device to be implanted(or whether a particular size of the cervical disc replacement devicecan be implanted) into the distracted cervical intervertebral space.Preferably, for each cervical disc replacement device to be implanted, aplurality of sizes of the cervical disc replacement device would beavailable. Accordingly, preferably, each of the plurality of trials foruse with a particular plurality of differently sized cervical discreplacement devices would have a respective oval footprint and depthdimension set corresponding to the footprint and depth dimension set ofa respective one of the plurality of differently sized cervical discreplacement devices.

Each of the cervical disc replacement trials includes a distal endconfigured to approximate relevant dimensions of an available cervicaldisc replacement device. The distal end has a head with an ovalfootprint. The upper surface of the head is convex, similar to theconfiguration of the vertebral body contact surface of the upper elementof the cervical disc replacement device (but without the teeth). Thelower surface of the head is flat, similar to the configuration of thevertebral body contact surface of the lower element of the cervical discreplacement device (but without the teeth). The cervical discreplacement trial, not having the teeth, can be inserted and removedfrom the intervertebral space without compromising the endplatesurfaces. The cervical disc replacement trial further has a vertebralbody stop disposed at the anterior edge of the head, to engage theanterior surface of the upper vertebral body before the trial isinserted too far into the intervertebral space.

Accordingly, the surgeon can insert and remove at least one of thetrials (or more, as necessary) from the prepared intervertebral space.As noted above, the trials are useful for distracting the preparedintervertebral space. For example, starting with the largest distractorthat can be wedged in between the vertebral bones, the surgeon willinsert the trial head and then lever the trial handle up and down toloosen the annulus and surrounding ligaments to urge the bone fartherapart. The surgeon then removes the trial head from the intervertebralspace, and replaces it with the next largest (in terms of height) trialhead. The surgeon then levers the trial handle up and down to furtherloosen the annulus and ligaments. The surgeon then proceeds to removeand replace the trial head with the next largest (in terms of height)trial head, and continues in this manner with larger and larger trialsuntil the intervertebral space is distracted to the appropriate height.

Regardless of the distraction method used, the cervical disc replacementtrials are useful for finding the cervical disc replacement device sizethat is most appropriate for the prepared intervertebral space, becauseeach of the trial heads approximates the relevant dimensions of anavailable cervical disc replacement device. Once the intervertebralspace is distracted, the surgeon can insert and remove one or more ofthe trial heads to determine the appropriate size of cervical discreplacement device to use. Once the appropriate size is determined, thesurgeon proceeds to implant the selected cervical disc replacementdevice.

An insertion plate of the present invention is mounted to the cervicaldisc replacement device to facilitate a preferred simultaneousimplantation of the upper and lower elements of the replacement device.The upper and lower elements are held by the insertion plate in analigned configuration preferable for implantation. A ledge on the platemaintains a separation between the anterior portions of the inwardlyfacing surfaces of the elements to help establish and maintain thispreferred relationship. The flanges of the elements each have a mountingscrew hole and the insertion plate has two corresponding mounting holes.Mounting screws are secured through the colinear mounting screw holepairs, such that the elements are immovable with respect to theinsertion plate and with respect to one another. In this configuration,the upper element, lower element, and insertion plate construct ismanipulatable as a single unit.

An insertion handle of the present invention is provided primarily forengaging an anteriorly extending stem of the insertion plate so that thecervical disc replacement device and insertion plate construct can bemanipulated into and within the treatment site. The insertion handle hasa shaft with a longitudinal bore at a distal end and a flange at aproximal end. Longitudinally aligning the insertion handle shaft withthe stem, and thereafter pushing the hollow distal end of the insertionhandle shaft toward the insertion plate, causes the hollow distal end tofriction-lock to the outer surface of the stem. Once the insertionhandle is engaged with the insertion plate, manipulation of theinsertion handle shaft effects manipulation of the cervical discreplacement device and insertion plate construct. The surgeon cantherefore insert the construct into the treatment area. Moreparticularly, after the surgeon properly prepares the intervertebralspace, the surgeon inserts the cervical disc replacement device into theintervertebral space from an anterior approach, such that the upper andlower elements are inserted between the adjacent vertebral bones withthe element footprints fitting within the perimeter of theintervertebral space and with the teeth of the elements' vertebral bodycontact surfaces engaging the vertebral endplates, and with the flangesof the upper and lower elements flush against the anterior faces of theupper and lower vertebral bones, respectively.

Once the construct is properly positioned in the treatment area, thesurgeon uses an insertion pusher of the present invention to disengagethe insertion handle shaft from the stem of the insertion plate. Theinsertion pusher has a longitudinal shaft with a blunt distal end and aproximal end with a flange. The shaft of the insertion pusher can beinserted into and translated within the longitudinal bore of theinsertion handle shaft. Because the shaft of the insertion pusher is aslong as the longitudinal bore of the insertion handle shaft, the flangeof the insertion handle and the flange of the insertion pusher areseparated by a distance when the pusher shaft is inserted all the wayinto the longitudinal bore until the blunt distal end of the shaftcontacts the proximal face of the insertion plate stem. Accordingly, abringing together of the flanges (e.g., by the surgeon squeezing theflanges toward one another) will overcome the friction lock between thedistal end of the insertion handle shaft and the stem of the insertionplate.

Once the insertion handle has been removed, the surgeon uses a drillguide of the present invention to guide the surgeon's drilling of bonescrews through the bone screw holes of the upper and lower elements'flanges and into the vertebral bones. The drill guide has a longitudinalshaft with a distal end configured with a central bore that accommodatesthe stem so that the drill guide can be placed on and aligned with thestem. The distal end is further configured to have two guide bores thathave respective longitudinal axes at preferred bone screw drilling pathsrelative to one another. When the central bore is disposed on the stemof the insertion plate, the drill guide shaft can be rotated on the steminto either of two preferred positions in which the guide bores arealigned with the bone screw holes on one of the flanges, or with thebone screw holes on the other flange.

To secure the upper element flange to the upper vertebral body, thesurgeon places the drill guide shaft onto the stem of the insertionplate, and rotates the drill guide into the first preferred position.Using a suitable bone drill and cooperating drill bit, the surgeondrills upper tap holes for the upper bone screws. The surgeon thenrotates the drill guide shaft on the stem of the insertion plate untilthe guide bores no longer cover the upper bone screw holes. The surgeoncan then screw the upper bone screws into the upper tap holes using asuitable surgical bone screw driver. To then secure the lower elementflange to the lower vertebral body, the surgeon further rotates thedrill guide shaft on the stem of the insertion plate until the drillguide is in the second preferred position, and proceeds to drill thelower bone screw tap holes and screw the lower bone screws into them inthe same manner.

Once the upper and lower elements are secured to the adjacent vertebralbones, the surgeon removes the drill guide from the stem of theinsertion plate and from the treatment area. Using a suitable surgicalscrew driver, the surgeon then removes the mounting screws that hold theinsertion plate against the elements' flanges and removes the insertionplate and the mounting screws from the treatment area.

Once the mounting screws and the insertion plate are removed, thesurgeon uses a clip applicator of the present invention to mountretaining clips on the flanges to assist in retaining the bone screws.Each of the clips has a central attachment bore and, extendingtherefrom, a pair of oppositely directed laterally extending flanges andan upwardly (or downwardly) extending hooked flange. The clips can besnapped onto the element flanges (one clip onto each flange). Each ofthe laterally extending flanges of the clip is sized to cover at least aportion of a respective one of the bone screw heads when the clip isattached in this manner to the flange so that the clips help prevent thebone screws from backing out. In an alternate embodiment, the retainingdevice comprises a threaded member and a head flange member, thethreaded member received into the threaded opening of the mounting screwholes left by the removal of the mounting screws and the insertionplate. The head flange defined by an outer perimeter, and extending fromthe threaded attachment member. The head flange is in part abuttinglyreceived against a side of the flange of the intervertebral discreplacement device and the outer perimeter is partially received over aportion of the at least one bone screw to prevent the at least one bonescrew from backing out of the at least one bone screw hole when theretaining device is fully engaged with the intervertebral discreplacement device. The head flange includes a solid portion and atleast one stress relief area wholly contained within the confines of andnot extending through the outer perimeter so that the at least onestress relief area is bounded on all lateral sides by the solid portion.The at least one stress relief located on the head flange at a pointother than a central point of the head flange and providing for the headflange to be at least somewhat flexible in a substantially axialdirection of the threaded attachment member. In a preferred embodiment,the head flange includes four circular stress relief areas.

Also disclosed is an alternate dual cervical disc replacement deviceconfiguration suitable, for example, for implantation into two adjacentcervical intervertebral spaces. The configuration includes an alternate,upper, cervical disc replacement device (including an upper element andan alternate lower element), for implantation into an upper cervicalintervertebral space, and further includes an alternate, lower, cervicaldisc replacement device (including an alternate upper element and alower element), for implantation into an adjacent, lower, cervicalintervertebral space. The illustrated alternate, upper, embodiment isidentical in structure to the cervical disc replacement device of FIGS.1 a-3 f, with the exception that the flange of the lower element isconfigured differently and without bone screw holes. The illustratedalternate, lower, embodiment is identical in structure to the cervicaldisc replacement device of FIGS. 1 a-3 f, with the exception that theflange of the upper element is configured differently and without bonescrew holes.

More particularly, in the alternate, upper, cervical disc replacementdevice of this alternate configuration, the flange of the alternatelower element does not have bone screw holes, but does have a mountingscrew hole for attaching the alternate lower element to an alternate,upper, insertion plate. Similarly, in the alternate, lower, cervicaldisc replacement device of this alternate configuration, the flange ofthe alternate upper element does not have bone screw holes, but doeshave a mounting screw hole for attaching the alternate upper element toan alternate, lower, insertion plate. The extent of the flange of thealternate lower element is laterally offset to the right (in an anteriorview) from the midline, and the extent of the flange of the alternateupper element is laterally offset to the left (in an anterior view) fromthe midline, so that the flanges avoid one another when the alternatelower element of the alternate, upper, cervical disc replacement device,and the alternate upper element of the alternate, lower, cervical discreplacement device, are implanted in this alternate configuration.

The alternate, upper, insertion plate is identical in structure to theinsertion plate described above, with the exception that the lowerflange is offset from the midline (to the right in an anterior view) toalign its mounting screw hole with the offset mounting screw hole of thealternate lower element. Similarly, the alternate, lower, insertionplate is identical in structure to the insertion plate described above,with the exception that the upper flange is offset from the midline (tothe left in an anterior view) to align its mounting screw hole with theoffset mounting screw hole of the alternate upper element.

Accordingly, the upper and lower elements of the alternate, upper,cervical disc replacement device, being held by the alternate upperinsertion plate, as well as the upper and lower elements of thealternate, lower, cervical disc replacement device, being held by thealternate lower insertion plate, can be implanted using the insertionhandle, insertion pusher, drill guide, clips (one on the uppermostelement flange, and one on the lowermost element flange, because onlythe uppermost element and the lowermost element are secured by bonescrews), and clip applicator, in the manner described above with respectto the implantation of the cervical disc replacement device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a-c show anterior (FIG. 1 a), lateral (FIG. 1 b), and bottom(FIG. 1 c) views of a top element of a cervical disc replacement deviceof the invention.

FIGS. 2 a-c show anterior (FIG. 2 a), lateral (FIG. 2 b), and top (FIG.2 c) views of a bottom element of the cervical disc replacement device.

FIGS. 3 a-f show top (FIG. 3 a), lateral (FIG. 3 b), anterior (FIG. 3c), posterior (FIG. 3 d), antero-lateral perspective (FIG. 3 e), andpostero-lateral perspective (FIG. 3 f) views of the cervical discreplacement device, assembled with the top and bottom elements of FIGS.1 a-c and 2 a-c.

FIGS. 4 a-g show top (FIG. 4 a), lateral (FIG. 4 b), anterior (FIG. 4c), posterior (FIG. 4 d), antero-lateral perspective (head only) (FIG. 4e), and postero-lateral perspective (head only) (FIG. 4 f) views of acervical disc replacement trial of the present invention.

FIGS. 5 a-d show top (FIG. 5 a), lateral (FIG. 5 b), anterior (FIG. 5c), and posterior (FIG. 5 d) views of an insertion plate of theinsertion instrumentation of the present invention. FIGS. 5 e and 5 fshow anterior (FIG. 5 e) and antero-lateral perspective (FIG. 5 f) viewsof the insertion plate mounted to the cervical disc replacement device.

FIGS. 6 a-d show top (FIG. 6 a), lateral (FIG. 6 b), anterior (FIG. 6c), and postero-lateral (FIG. 6 d) views of an insertion handle of theinsertion instrumentation of the present invention. FIG. 6 e shows anantero-lateral perspective view of the insertion handle attached to theinsertion plate. FIG. 6 f shows a magnified view of the distal end ofFIG. 6 e.

FIGS. 7 a-c show top (FIG. 7 a), lateral (FIG. 7 b), and anterior (FIG.7 c) views of an insertion pusher of the insertion instrumentation ofthe present invention. FIG. 7 d shows an antero-lateral perspective viewof the insertion pusher inserted into the insertion handle. FIG. 7 eshows a magnified view of the proximal end of FIG. 7 d.

FIGS. 8 a-c show top (FIG. 8 a), lateral (FIG. 8 b), and anterior (FIG.8 c) views of a drill guide of the insertion instrumentation of thepresent invention. FIG. 8 d shows an antero-lateral perspective view ofthe drill guide inserted onto the insertion plate. FIG. 8 e shows amagnified view of the distal end of FIG. 8 d.

FIG. 9 a shows an antero-lateral perspective view of the cervical discreplacement device implantation after bone screws have been applied andbefore the insertion plate has been removed. FIG. 9 b shows anantero-lateral perspective view of the cervical disc replacement deviceafter bone screws have been applied and after the insertion plate hasbeen removed.

FIGS. 10 a-f show top (FIG. 10 a), lateral (FIG. 10 b), posterior (FIG.10 c), anterior (FIG. 10 d), postero-lateral (FIG. 10 e), andantero-lateral (FIG. 10 f) views of a retaining clip of the presentinvention.

FIGS. 11 a-c show top (FIG. 11 a), lateral (FIG. 11 b), and anterior(FIG. 11 c) views of a clip applicator of the insertion instrumentationof the present invention. FIG. 11 d shows a postero-lateral perspectiveview of the clip applicator holding two retaining clips. FIG. 11 e showsan antero-lateral perspective view of FIG. 11 d.

FIG. 12 a shows the clip applicator applying the retaining clips to thecervical disc replacement device. FIGS. 12 b-h show anterior (FIG. 12b), posterior (FIG. 12 c), top (FIG. 12 d), bottom (FIG. 12 e), lateral(FIG. 12 f), antero-lateral perspective (FIG. 12 g), and postero-lateralperspective (FIG. 12 h) views of the cervical disc replacement deviceafter the retaining clips have been applied.

FIGS. 13 a-b show a prior art one level cervical fusion plate inanterior (FIG. 13 a) and lateral (FIG. 13 b) views. FIGS. 13 c-d show aprior art two level cervical fusion plate in anterior (FIG. 13 c) andlateral (FIG. 13 d) views.

FIGS. 14 a-e show an alternate, dual cervical disc replacement deviceconfiguration and alternate insertion plates for use therewith, inexploded perspective (FIG. 14 a), anterior (FIG. 14 b), posterior (FIG.14 c), lateral (FIG. 14 d), and collapsed perspective (FIG. 14 e) views.

FIGS. 15 a-c show an alternate upper element of the configuration ofFIGS. 14 a-e, in posterior (FIG. 15 a), anterior (FIG. 15 b), andantero-lateral (FIG. 15 c) views.

FIGS. 16 a-c show an alternate lower element of the configuration ofFIGS. 14 a-e, in posterior (FIG. 16 a), anterior (FIG. 16 b), andantero-lateral (FIG. 16 c) views.

FIGS. 17 a-c show an alternate, upper, insertion plate of theconfiguration of FIGS. 14 a-e in anterior (FIG. 17 a), posterior (FIG.17 b), and antero-lateral (FIG. 17 c) views.

FIGS. 18 a-c show an alternate, lower, insertion plate of theconfiguration of FIGS. 14 a-e in anterior (FIG. 18 a), posterior (FIG.18 b), and antero-lateral (FIG. 18 c) views.

FIGS. 19 a-c show an alternate retaining device for the bone screws inantero-lateral perspective partial assembly (FIG. 19 a), top assembly(FIG. 19 b) and top (FIG. 19 c) views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the invention will be described more fully hereinafter withreference to the accompanying drawings, it is to be understood at theoutset that persons skilled in the art may modify the invention hereindescribed while achieving the functions and results of the invention.Accordingly, the descriptions that follow are to be understood asillustrative and exemplary of specific structures, aspects and featureswithin the broad scope of the invention and not as limiting of suchbroad scope. Like numbers refer to similar features of like elementsthroughout.

A preferred embodiment of a cervical disc replacement device of thepresent invention, for use with the instrumentation of the presentinvention, will now be described.

Referring now to FIGS. 1 a-3 f, a top element 500 of the cervical discreplacement device 400 is shown in anterior (FIG. 1 a), lateral (FIG. 1b), and bottom (FIG. 1 c) views; a bottom element 600 of the cervicaldisc replacement device 400 is shown in anterior (FIG. 2 a), lateral(FIG. 2 b), and top (FIG. 2 c) views; and an assembly 400 of the top andbottom elements 500,600 is shown in top (FIG. 3 a), lateral (FIG. 3 b),anterior (FIG. 3 c), posterior (FIG. 3 d), antero-lateral perspective(FIG. 3 e), and postero-lateral perspective (FIG. 3 f) views.

The cervical disc replacement device 400 is an alternate embodiment ofthe cervical disc replacement device of the '702 application. Theillustrated alternate embodiment of the cervical disc replacement deviceis identical in structure to the cervical disc replacement device 100 inthe '702 application (and thus like components are like numbered, but inthe 400s rather than the 100s, in the 500s rather than the 200s, and inthe 600s rather than the 300s), with the exception that the vertebralbone attachment flanges are configured differently, such that they aresuitable for engagement by the instrumentation described herein. (Itshould be noted that, while the '702 application illustrated anddescribed the cervical disc replacement device 100 as having an upperelement flange 506 with two bone screw holes 508 a,508 b, and a lowerelement flange 606 with one bone screw hole 608, the '702 applicationexplained that the number of holes and the configuration of the flangescould be modified without departing from the scope of the invention asdescribed in the '702 application.)

More particularly, in this alternate embodiment, the upper element 500of the cervical disc replacement device 400 has a vertebral bodyattachment structure (e.g., a flange) 506 that preferably extendsupwardly from the anterior edge of the upper element 500, and preferablyhas a lateral curvature that approximates the curvature of the anteriorperiphery of the upper vertebral body against which it is to be secured.The attachment flange 506 is preferably provided with a flat recess 507,centered on the midline, that accommodates a clip 1150 a (describedbelow) of the present invention. The attachment flange 506 is furtherprovided with at least one (e.g., two) bone screw holes 508 a,508 b,preferably symmetrically disposed on either side of the midline.Preferably, the holes 508 a,508 b have longitudinal axes directed alongpreferred bone screw driving lines. For example, in this alternateembodiment, the preferred bone screw driving lines are angled upwardlyat 5 degrees and inwardly (toward one another) at 7 degrees (a total of14 degrees of convergence), to facilitate a toenailing of the bonescrews (described below and shown in FIGS. 12 a-h). Centrally betweenthe bone screw holes 508 a,508 b, at least one mounting feature (e.g., amounting screw hole) 509 is provided for attaching the upper element 500to an insertion plate 700 (described below) for implantation.

Similarly, in this alternate embodiment, the lower element 600 of thecervical disc replacement device 400 also has a vertebral bodyattachment structure (e.g., an oppositely directed and similarlyconfigured vertebral body attachment flange) 606 that preferably extendsdownwardly from the anterior edge of the lower element 600, andpreferably has a lateral curvature that approximates the curvature ofthe anterior periphery of the lower vertebral body against which it isto be secured. The attachment flange 606 is preferably provided with aflat recess 607, centered on the midline, that accommodates a clip 1150b (described below) of the present invention. The attachment flange 606is further provided with at least one (e.g., two) bone screw holes 608a,608 b, preferably symmetrically disposed on either side of themidline. Preferably, the holes 608 a,608 b have longitudinal axesdirected along preferred bone screw driving lines. For example, in thisalternate embodiment, the preferred bone screw driving lines are angleddownwardly at 5 degrees and inwardly (toward one another) at 7 degrees(a total of 14 degrees of convergence), to facilitate a toenailing ofthe bone screws (described below and shown in FIGS. 12 a-h). Centrallybetween the bone screw holes 608 a,608 b, at least one mounting feature(e.g., a mounting screw hole) 609 is provided for attaching the lowerelement 600 to the insertion plate 700 (described below) forimplantation.

Prior to implantation of the cervical disc replacement device, thesurgeon will prepare the intervertebral space. Typically, this willinvolve establishing access to the treatment site, removing the damagednatural intervertebral disc, preparing the surfaces of the endplates ofthe vertebral bones adjacent the intervertebral space, and distractingthe intervertebral space. (It should be noted that the cervical discreplacement device of the present invention, and the instrumentation andimplantation methods described herein, require minimal if any endplatepreparation.) More particularly, after establishing access to thetreatment site, the surgeon will remove the natural disc material,preferably leaving as much as possible of the annulus intact. Then, thesurgeon will remove the anterior osteophyte that overhangs the mouth ofthe cervical intervertebral space, and any lateral osteophytes that mayinterfere with the placement of the cervical disc replacement device orthe movement of the joint. Using a burr tool, the surgeon will thenensure that the natural lateral curvature of the anterior faces of thevertebral bodies is uniform, by removing any surface anomalies thatdeviate from the curvature. Also using the burr tool, the surgeon willensure that the natural curvature of the endplate surface of the uppervertebral body, and the natural flatness of the endplate surface of thelower vertebral body, are uniform, by removing any surface anomaliesthat deviate from the curvature or the flatness. Thereafter, the surgeonwill distract the intervertebral space to the appropriate height forreceiving the cervical disc replacement device. Any distraction tool ormethod known in the art, e.g., a Caspar Distractor, can be used toeffect the distraction and/or hold open the intervertebral space.Additionally or alternatively, the cervical disc replacement trials ofthe present invention can be used to distract the intervertebral space(as described below).

Referring now to FIGS. 4 a-f, a cervical disc replacement trial 1200 ofthe present invention is shown in top (FIG. 4 a), lateral (FIG. 4 b),lateral (head only) (FIG. 4 c), posterior (FIG. 4 d), anterior (FIG. 4e), antero-lateral perspective (head only) (FIG. 4 f), andpostero-lateral perspective (head only) (FIG. 4 g) views.

Preferably, a plurality of cervical disc replacement trials are providedprimarily for use in determining the appropriate size of a cervical discreplacement device to be implanted (or whether a particular size of thecervical disc replacement device can be implanted) into the distractedcervical intervertebral space (e.g., the cervical disc replacementdevice 400 of FIGS. 1 a-3 f). Preferably, for each cervical discreplacement device to be implanted, a plurality of sizes of the cervicaldisc replacement device would be available. That is, preferably, aplurality of the same type of cervical disc replacement device would beavailable, each of the plurality having a respective footprint and depthdimension combination that allows it to fit within a correspondinglydimensioned intervertebral space. For example, the plurality of cervicaldisc replacement devices could include cervical disc replacement deviceshaving oval footprints being 12 mm by 14 mm, 14 mm by 16 mm, or 16 mm by18 mm, and depths ranging from 6 mm to 14 mm in 1 mm increments, for atotal of 27 devices. Accordingly, preferably, each of the plurality oftrials for use with a particular plurality of differently sized cervicaldisc replacement devices would have a respective oval footprint anddepth dimension set corresponding to the footprint and depth dimensionset of a respective one of the plurality of differently sized cervicaldisc replacement devices. For example, the plurality of trials for usewith the set of cervical disc replacement devices described, forexample, could include trials having oval footprints being 12 mm by 14mm, 14 mm by 16 mm, or 16 mm by 18 mm, and depths ranging from 6 mm to14 mm in 1 mm increments, for a total of 27 static trials. It should beunderstood that the cervical disc replacement devices and/or the trialscan be offered in a variety of dimensions without departing from thescope of the invention, and that the dimensions specifically identifiedand quantified herein are merely exemplary. Moreover, it should beunderstood that the set of trials need not include the same number oftrials for each cervical disc replacement device in the set of cervicaldisc replacement devices, but rather, none, one, or more than one trialcan be included in the trial set for any particular cervical discreplacement device in the set.

Each of the cervical disc replacement trials (the cervical discreplacement trial 1200 shown in FIGS. 4 a-g is exemplary for all of thetrials in the plurality of trials; preferably the trials in theplurality of trials differ from one another only with regard to certaindimensions as described above) includes a shaft 1202 having a configureddistal end 1204 and a proximal end having a handle 1206. Preferably, theproximal end is provided with a manipulation features (e.g., a hole1216) to, e.g., decrease the weight of the trial 1200, facilitatemanipulation of the trial 1200, and provide a feature for engagement byan instrument tray protrusion. The distal end is configured toapproximate relevant dimensions of the cervical disc replacement device.More particularly in the illustrated embodiment (for example), thedistal end 1204 has a trial configuration (e.g., a head 1208 having anoval footprint dimensioned at 12 mm by 14 mm, and a thickness of 6 mm).The upper surface 1210 of the head 1208 is convex, similar to theconfiguration of the vertebral body contact surface of the upper element500 of the cervical disc replacement device 400 (but without the teeth).The lower surface 1212 of the head 1208 is flat, similar to theconfiguration of the vertebral body contact surface of the lower element600 of the cervical disc replacement device 400 (but without the teeth).The illustrated embodiment, therefore, with these dimensions,approximates the size of a cervical disc replacement device having thesame height and footprint dimensions. The cervical disc replacementtrial, not having the teeth, can be inserted and removed from theintervertebral space without compromising the endplate surfaces. Thecervical disc replacement trial 1200 further has an over-insertionprevention features (e.g., a vertebral body stop 1214) preferablydisposed at the anterior edge of the head 1208, to engage the anteriorsurface of the upper vertebral body before the trial 1200 is insertedtoo far into the intervertebral space. The body of the trial 1200preferably has one or more structural support features (e.g., a rib 1216extending anteriorly from the head 1208 below the shaft 1202) thatprovides stability, e.g., to the shaft 1202 for upward and downwardmovement, e.g., if the head 1208 must be urged into the intervertebralspace by moving the shaft 1202 in this manner. Further, preferably asshown, the head 1208 is provided with an insertion facilitation features(e.g., a taper, decreasing posteriorly) to facilitate insertion of thehead 1208 into the intervertebral space by, e.g., acting as a wedge tourge the vertebral endplates apart. Preferably, as shown, the uppersurface 1210 is fully tapered at approximately 5 degrees, and the distalhalf of the lower surface 1212 is tapered at approximately 4 degrees.

Accordingly, the surgeon can insert and remove at least one of thetrials (or more, as necessary) from the prepared intervertebral space.As noted above, the trials are useful for distracting the preparedintervertebral space. For example, starting with the largest distractorthat can be wedged in between the vertebral bones, the surgeon willinsert the trial head 1208 (the tapering of the trial head 1208facilitates this insertion by acting as a wedge to urge the vertebralendplates apart), and then lever the trial handle 1206 up and down toloosen the annulus and surrounding ligaments to urge the bone fartherapart. Once the annulus and ligaments have been loosened, the surgeonremoves the trial head 1208 from the intervertebral space, and replacesit with the next largest (in terms of height) trial head 1208. Thesurgeon then levers the trial handle 1206 up and down to further loosenthe annulus and ligaments. The surgeon then proceeds to remove andreplace the trial head 1208 with the next largest (in terms of height)trial head 1208, and continues in this manner with larger and largertrials until the intervertebral space is distracted to the appropriateheight. This gradual distraction method causes the distractedintervertebral space to remain at the distracted height with minimalsubsidence before the cervical disc replacement device is implanted. Theappropriate height is one that maximizes the height of theintervertebral space while preserving the annulus and ligaments.

Regardless of the distraction method used, the cervical disc replacementtrials are useful for finding the cervical disc replacement device sizethat is most appropriate for the prepared intervertebral space, becauseeach of the trial heads approximates the relevant dimensions of anavailable cervical disc replacement device. Once the intervertebralspace is distracted, the surgeon can insert and remove one or more ofthe trial heads to determine the appropriate size of cervical discreplacement device to use. Once the appropriate size is determined, thesurgeon proceeds to implant the selected cervical disc replacementdevice.

A preferred method of, and instruments for use in, implanting thecervical disc replacement device will now be described.

Referring now to FIGS. 5 a-f, an insertion plate 700 of the insertioninstrumentation of the present invention is shown in top (FIG. 5 a),lateral (FIG. 5 b), anterior (FIG. 5 c), and posterior (FIG. 5 d) views.FIGS. 5 e and 5 f show anterior (FIG. 5 e) and antero-lateralperspective (FIG. 5 f) views of the insertion plate 700 mounted to thecervical disc replacement device 400.

The insertion plate 700 has a base 702 with a first mounting area 704 a(preferably an upwardly extending flange) and a second mounting area 704b (preferably a downwardly extending flange), and a primary attachmentfeature (e.g., an anteriorly extending central stem) 706. The connectionof the stem 706 to the base 702 preferably includes an axial rotationprevention feature, e.g., two oppositely and laterally extending keyflanges 708 a,708 b. The stem 706 preferably has a proximal portion 710that is tapered to have a decreasing diameter away from the base 702.That is, the tapered proximal portion 710 has an initial smallerdiameter that increases toward the base 702 gradually to a final largerdiameter. The base 702 preferably has a posteriorly extending ledge 716that has a flat upper surface and a curved lower surface.

The insertion plate 700 is mounted to the cervical disc replacementdevice 400 to facilitate the preferred simultaneous implantation of theupper and lower elements 500,600. The upper and lower elements 500,600are held by the insertion plate 700 in a preferred relationship to oneanother that is suitable for implantation. More particularly, as shownin FIGS. 3 a-f, 5 e, and 5 f, the elements 500,600 are preferablyaxially rotationally aligned with one another, with the elementperimeters and flanges 506,606 axially aligned with one another, andheld with the bearing surfaces 512,612 in contact. The ledge 716maintains a separation between the anterior portions of the inwardlyfacing surfaces of the elements 500,600 to help establish and maintainthis preferred relationship, with the flat upper surface of the ledge716 in contact with the flat anterior portion of the inwardly facingsurface of the upper element 500, and the curved lower surface of theledge 716 in contact with the curved anterior portion of the inwardlyfacing surface of the lower element 600.

While any suitable method or mechanism can be used to mount the elements500,600 to the insertion plate 700, a preferred arrangement isdescribed. That is, it is preferred, as shown and as noted above, thatthe flanges 506,606 of the elements 500,600 (in addition to having thebone screw holes 508 a,508 b,608 a,608 b described above) each have atleast one mounting feature (e.g., mounting screw hole 509,609), and theinsertion plate 700 has two (at least two, each one alignable with arespective mounting screw hole 509,609) corresponding mounting features(e.g., mounting screw holes 712 a,712 b), spaced to match the spacing of(and each be colinear with a respective one of) the mounting screw holes509,609 on the flanges 506,606 of the elements 500,600 of the cervicaldisc replacement device 400 when those elements 500,600 are disposed inthe preferred relationship for implantation. Accordingly, mountingscrews 714 a,714 b or other suitable fixation devices are securedthrough the colinear mounting screw hole pairs 509,712 a and 609,712 b(one screw through each pair), such that the elements 500,600 areimmovable with respect to the insertion plate 700 and with respect toone another. Thus, in this configuration, the upper element 500, lowerelement 600, and insertion plate 700 construct is manipulatable as asingle unit.

Preferably, for each size of cervical disc replacement device, thedescribed configuration is established (and rendered sterile in ablister pack through methods known in the art) prior to delivery to thesurgeon. That is, as described below, the surgeon will simply need toopen the blister pack and apply the additional implantation tools to theconstruct in order to implant the cervical disc replacement device.Preferably, the configuration or dimensions of the insertion plate canbe modified (either by providing multiple different insertion plates, orproviding a single dynamically modifiable insertion plate) toaccommodate cervical disc replacement devices of varying heights. Forexample, the positions of the mounting screw holes 712 a,712 b on theflanges 704 a,704 b can be adjusted (e.g., farther apart for replacementdevices of greater height, and close together for replacement devices oflesser height), and the size of the flanges 704 a,70 b can be adjustedto provide structural stability for the new hole positions. Preferably,in other respects, the insertion plate configuration and dimensions neednot be modified, to facilitate ease of manufacturing and lowermanufacturing costs.

It should be noted that the described configuration of the constructpresents the cervical disc replacement device to the surgeon in afamiliar manner. That is, by way of explanation, current cervical fusionsurgery involves placing a fusion device (e.g., bone or a porous cage)in between the cervical intervertebral bones, and attaching a cervicalfusion plate to the anterior aspects of the bones. Widely used cervicalfusion devices (an example single level fusion plate 1300 is shown inanterior view in FIG. 13 a and in lateral view in FIG. 13 b) areconfigured with a pair of laterally spaced bone screw holes 1302 a,1302b on an upper end 1304 of the plate 1300, and a pair of laterally spacedbone screw holes 1306 a,1306 b on a lower end 1308 of the plate 1300. Toattach the plate 1300 to the bones, two bone screws are disposed throughthe upper end's bone screw holes 1302 a,1302 b and into the upper bone,and two bone screws are disposed through the lower end's bone screwholes 1306 a,1306 b and into the lower bone. This prevents the bonesfrom moving relative to one another, and allows the bones to fuse to oneanother with the aid of the fusion device.

Accordingly, as can be seen in FIG. 5 e, when the upper and lowerelements 500,600 of the cervical disc replacement device 400 are held inthe preferred spatial relationship, the flanges 506,606 of the elements500,600, and their bone screw holes 508 a,508 b, present to the surgeona cervical hardware and bone screw hole configuration similar to afamiliar cervical fusion plate configuration. The mounting of theelements 500,600 to the insertion plate 700 allows the elements 500,600to be manipulated as a single unit for implantation (by manipulating theinsertion plate 700), similar to the way a cervical fusion plate ismanipulatable as a single unit for attachment to the bones. This aspectof the present invention simplifies and streamlines the cervical discreplacement device implantation procedure.

As noted above, the cervical disc replacement device 400 and insertionplate 700 construct is preferably provided sterile (e.g., in a blisterpack) to the surgeon in an implant tray (the tray preferably beingfilled with constructs for each size of cervical disc replacementdevice). The construct is preferably situated in the implant tray withthe stem 706 of the insertion plate 700 facing upwards for readyacceptance of the insertion handle 800 (described below).

Referring now to FIGS. 6 a-e, an insertion handle 800 of the insertioninstrumentation of the present invention is shown in top (FIG. 6 a),lateral (FIG. 6 b), anterior (FIG. 6 c), and postero-lateral (distal endonly) (FIG. 6 d) views. FIG. 6 e shows an antero-lateral perspectiveview of the insertion handle 800 attached to the stem 706 of theinsertion plate 700. FIG. 6 f shows a magnified view of the distal endof FIG. 6 e.

The insertion handle 800 is provided primarily for engaging the stem 706of the insertion plate 700 so that the cervical disc replacement device400 and insertion plate 700 construct can be manipulated into and withinthe treatment site. The insertion handle 800 has a shaft 802 with anattachment feature (e.g., a longitudinal bore) 804 at a distal end 806and a manipulation feature (e.g., a flange) 810 at a proximal end 808.Preferably, the longitudinal bore 804 has an inner taper at the distalend 806 such that the inner diameter of the distal end 806 decreasestoward the distal end 806, from an initial larger inner diameter at aproximal portion of the distal end 806 to a final smaller inner diameterat the distal edge of the distal end 806. The distal end 806 alsopreferably has an axial rotation prevention feature, e.g., two (at leastone) key slots 814 a,814 b extending proximally from the distal end 806.Each slot 814 a,814 b is shaped to accommodate the key flanges 708 a,708b at the connection of the base 702 to the stem 706 when the distal end806 is engaged with the stem 706. The material from which the insertionhandle 800 is formed (preferably, e.g., Ultem™), and also the presenceof the key slots 814 a,814 b, permits the diameter of the hollow distalend 806 to expand as needed to engage the tapered stem 706 of theinsertion plate 700. More particularly, the resting diameter (prior toany expansion) of the hollow distal end 806 of the insertion handle 800is incrementally larger than the initial diameter of the taperedproximal portion 710 of the stem 706 of the insertion plate 700, andincrementally smaller than the final diameter of the tapered proximalportion 710 of the stem 706 of the insertion plate 700. Accordingly,longitudinally aligning the insertion handle shaft 802 with the stem706, and thereafter pushing the hollow distal end 806 of the insertionhandle shaft 802 toward the insertion plate 700, causes the hollowdistal end 806 to initially readily encompass the tapered proximalportion 710 of the stem 706 (because the initial diameter of the taperedproximal portion 710 is smaller than the resting diameter of the hollowtapered distal end 806). With continued movement of the insertion handleshaft 802 toward the insertion plate base 702, the hollow distal end 806is confronted by the increasing diameter of the tapered proximal portion710. Accordingly, the diameter of the hollow distal end 806 expands (bypermission of the shaft 802 body material and the key slots 814 a,814 bas the slots narrow) under the confrontation to accept the increasingdiameter. Eventually, with continued movement under force, the innersurface of the hollow distal end 806 is friction-locked to the outersurface of the tapered proximal portion 710. Each of the key slots 814a,814 b straddles a respective one of the key flanges 708 a,708 b at theconnection of the base 702 to the stem 706. This enhances the ability ofthe insertion handle 800 to prevent rotation of the insertion handleshaft 802 relative to the insertion plate 700 (about the longitudinalaxis of the insertion handle shaft 802). It should be understood thatother methods or mechanisms of establishing engagement of the stem 706by the insertion handle 800 can be used without departing from the scopeof the invention.

Once the insertion handle 800 is engaged with the insertion plate 700,manipulation of the insertion handle shaft 802 effects manipulation ofthe cervical disc replacement device 400 and insertion plate 700construct. The surgeon can therefore remove the construct from theimplant tray, and insert the construct into the treatment area. Moreparticularly, according to the implantation procedure of the invention,after the surgeon properly prepares the intervertebral space (removesthe damaged natural disc, modifies the bone surfaces that define theintervertebral space, and distracts the intervertebral space to theappropriate height), the surgeon inserts the cervical disc replacementdevice 400 into the intervertebral space from an anterior approach, suchthat the upper and lower elements 500,600 are inserted between theadjacent vertebral bones with the element footprints fitting within theperimeter of the intervertebral space and with the teeth of theelements' vertebral body contact surfaces 502,602 engaging the vertebralendplates, and with the flanges 506,606 of the upper and lower elements500,600 flush against the anterior faces of the upper and lowervertebral bones, respectively. (As discussed above, the flanges 506,606preferably have a lateral curvature that approximates the lateralcurvature of the anterior faces of the vertebral bones.)

Referring now to FIGS. 7 a-e, an insertion pusher 900 of the insertioninstrumentation of the present invention is shown in top (FIG. 7 a),lateral (FIG. 7 b), and anterior (FIG. 7 c) views. FIG. 7 d shows anantero-lateral perspective view of the insertion pusher 900 insertedinto the insertion handle 800. FIG. 7 e shows a magnified view of theproximal end of FIG. 7 d.

Once the construct is properly positioned in the treatment area, thesurgeon uses the insertion pusher 900 to disengage the insertion handleshaft 802 from the stem 706 of the insertion plate 700. Moreparticularly, the insertion pusher 900 has a longitudinal shaft 902having a preferably blunt distal end 904 and a proximal end 906preferably having a flange 908. The shaft 902 of the insertion pusher900 has a diameter smaller than the inner diameter of the insertionhandle shaft 802, such that the shaft 902 of the insertion pusher 900can be inserted into and translated within the longitudinal bore 804 ofthe insertion handle shaft 802. (The longitudinal bore 804 preferably,for the purpose of accommodating the insertion pusher 900 and otherpurposes, extends the length of the insertion handle shaft 802.) Theshaft 902 of the insertion pusher 900 is preferably as long as (or,e.g., at least as long as) the longitudinal bore 804. Accordingly, toremove the insertion handle shaft 802 from the insertion plate 700, theshaft 902 of the insertion pusher 900 is inserted into the longitudinalbore 804 of the insertion handle shaft 802 and translated therein untilthe blunt distal end 904 of the pusher shaft 802 is against the proximalend of the tapered stem 706 of the insertion plate 700. Because theshaft 902 of the insertion pusher 900 is as long as the longitudinalbore 804 of the insertion handle shaft 802, the flange 810 of theinsertion handle 800 and the flange 908 of the insertion pusher 900 areseparated by a distance (see FIGS. 7 d and 7 e) that is equivalent tothe length of that portion of the stem 706 that is locked in the distalend 806 of the insertion handle shaft 802. Accordingly, a bringingtogether of the flanges 810,908 (e.g., by the surgeon squeezing theflanges 810,908 toward one another) will overcome the friction lockbetween the distal end 806 of the insertion handle shaft 802 and thestem 706 of the insertion plate 700, disengaging the insertion handleshaft 802 from the insertion plate 700 without disturbing thedisposition of the cervical disc replacement device 400 and insertionplate 700 construct in the treatment area.

Referring now to FIGS. 8 a-e, a drill guide 1000 of the insertioninstrumentation of the present invention is shown in top (FIG. 8 a),lateral (FIG. 8 b), and anterior (FIG. 8 c) views. FIG. 8 d shows anantero-lateral perspective view of the drill guide 1000 inserted ontothe stem 706 of the insertion plate 700. FIG. 8 e shows a magnified viewof the distal end of FIG. 8 d.

Once the insertion handle 800 has been removed, the surgeon uses thedrill guide 1000 to guide the surgeon's drilling of the bone screws(described below) through the bone screw holes 508 a,508 b and 608 a,608b of the upper 500 and lower 600 elements' flanges 506,606 and into thevertebral bones. More particularly, the drill guide 1000 has alongitudinal shaft 1002 having a configured distal end 1004 and aproximal end 1006 with a manipulation feature (e.g., lateral extensions1008 a,1008 b). The lateral extensions 1008 a,1008 b are useful formanipulating the shaft 1002. The distal end 1004 is configured to have ashaft guiding feature (e.g., a central bore 1010) suitable for guidingthe shaft 1002 in relation to the stem 706 of the insertion plate 700therethrough. For example, the central bore 1010 accommodates the stem706 so that the drill guide 1000 can be placed on and aligned with thestem 706. The longitudinal axis of the bore 1010 is preferably offsetfrom the longitudinal axis of the drill guide shaft 1002. The distal end1004 is further configured to have two guide bores 1012 a,1012 b thathave respective longitudinal axes at preferred bone screw drilling pathsrelative to one another. More particularly, the central bore 1010, drillguide shaft 1002, and guide bores 1012 a,1012 b, are configured on thedistal end 1004 of the drill guide 1000 such that when the central bore1010 is disposed on the stem 706 of the insertion plate 700 (see FIGS. 8d and 8 e), the drill guide shaft 1002 can be rotated on the stem 706into either of two preferred positions in which the guide bores 1012a,1012 b are aligned with the bone screw holes 508 a,508 b or 608 a,608b on either of the flanges 506 or 606. Stated alternatively, in a firstpreferred position (see FIGS. 8 d and 8 e), the drill guide 1000 can beused to guide bone screws through the bone screw holes 508 a,508 b inthe flange 506 of the upper element 500, and in a second preferredposition (in which the drill guide is rotated 180 degrees, about thelongitudinal axis of the stem 706, from the first preferred position),the same drill guide 1000 can be used to guide bone screws through thebone screw holes 608 a,608 b in the flange 606 of the lower element 600.When the drill guide 1000 is disposed in either of the preferredpositions, the longitudinal axes of the guide bores 1012 a,1012 b arealigned with the bone screw holes 508 a,508 b or 608 a,608 b on theflanges 506 or 606, and are directed along preferred bone screw drillingpaths through the bone screw holes.

Accordingly, to secure the upper element flange 506 to the uppervertebral body, the surgeon places the drill guide shaft 1002 onto thestem 706 of the insertion plate 700, and rotates the drill guide 1000into the first preferred position. Preferably, the surgeon then appliesan upward pressure to the drill guide 1000, urging the upper element 500tightly against the endplate of the upper vertebral body. Using asuitable bone drill and cooperating drill bit, the surgeon drills uppertap holes for the upper bone screws. Once the upper tap holes aredrilled, the surgeon rotates the drill guide shaft 1002 on the stem 706of the insertion plate 700 until the guide bores 1012 a,1012 b no longercover the upper bone screw holes 508 a,508 b. The surgeon can then screwthe upper bone screws into the upper tap holes using a suitable surgicalbone screw driver.

Additionally, to secure the lower element flange 606 to the lowervertebral body, the surgeon further rotates the drill guide shaft 1002on the stem 706 of the insertion plate 700 until the drill guide 1000 isin the second preferred position. Preferably, the surgeon then applies adownward pressure to the drill guide 1000, urging the lower element 600tightly against the endplate of the lower vertebral body. Using thesuitable bone drill and cooperating drill bit, the surgeon drills lowertap holes for the lower bone screws. Once the lower tap holes aredrilled, the surgeon rotates the drill guide shaft 1002 on the stem 706of the insertion plate 700 until the guide bores 1012 a,1012 b no longercover the lower bone screw holes 608 a,608 b. The surgeon can then screwthe lower bone screws into the lower tap holes using the suitablesurgical bone screw driver.

It should be noted that the bone screws (or other elements of theinvention) may include features or mechanisms that assist in preventscrew backup. Such features may include, but not be limited to, one ormore of the following: titanium plasma spray coating, bead blastedcoating, hydroxylapetite coating, and grooves on the threads.

Once the elements 500,600 are secured to the adjacent vertebral bones,the surgeon removes the drill guide 1000 from the stem 706 of theinsertion plate 700 and from the treatment area (see FIG. 9 a). Using asuitable surgical screw driver, the surgeon then removes the mountingscrews 714 a,714 b that hold the insertion plate 700 against theelements' flanges 506,606, and removes the insertion plate 700 and themounting screws 714 a,714 b from the treatment area (see FIG. 9 b).

Referring now to FIGS. 10 a-f, a retaining clip 1150 a of the presentinvention is shown in top (FIG. 10 a), lateral (FIG. 10 b), posterior(FIG. 10 c), anterior (FIG. 10 d), postero-lateral perspective (FIG. 10e), and antero-lateral perspective (FIG. 10 f) views. (The features ofretaining clip 1150 a are exemplary of the features of the like-numberedfeatures of retaining clip 1150 b, which are referenced by b's ratherthan a's.) Referring now to FIGS. 11 a-e, a clip applicator 1100 of theinsertion instrumentation of the present invention is shown in top (FIG.11 a), lateral (FIG. 11 b), and anterior (FIG. 11 c) views. FIG. 11 dshows a postero-lateral perspective view of the clip applicator 1100holding two retaining clips 1150 a,1150 b of the present invention. FIG.11 e shows an antero-lateral perspective view of FIG. 11 d. Referringnow to FIGS. 12 a-h, the clip applicator 1100 is shown applying theretaining clips 1150 a,1150 b to the cervical disc replacement device400. FIGS. 12 b-h show anterior (FIG. 12 b), posterior (FIG. 12 c), top(FIG. 12 d), bottom (FIG. 12 e), lateral (FIG. 12 f), antero-lateralperspective (FIG. 12 g), and postero-lateral perspective (FIG. 12 h)views of the cervical disc replacement device 400 after the retainingclips 1150 a,1150 b have been applied.

Once the mounting screws 714 a,714 b and the insertion plate 700 areremoved, the surgeon uses the clip applicator 1100 to mount theretaining clips 1150 a,1150 b on the flanges 506,606 to assist inretaining the bone screws. As shown in FIGS. 10 a-f, each of the clips1150 a,1150 b preferably has an applicator attachment feature (e.g., acentral attachment bore 1152 a,1152 b) and, extending therefrom, a pairof bone screw retaining features (e.g., oppositely directed laterallyextending flanges 1156 a,1156 b and 1158 a,1158 b) and a flangeattachment feature (e.g., an upwardly (or downwardly) extending hookedflange 1160 a,1160 b). The extent of the hook flange 1160 a,1160 b ispreferably formed to bend in toward the base of the hook flange 1160a,1160 b, such that the enclosure width of the formation is wider thanthe mouth width of the formation, and such that the extent is springbiased by its material composition toward the base. The enclosure widthof the formation accommodates the width of the body of a flange 506,606of the cervical disc replacement device 400, but the mouth width of theformation is smaller than the width of the flange 506,606. Accordingly,and referring now to FIGS. 12 b-h, each clip 1150 a,1150 b can beapplied to an element flange 506,606 such that the hook flange 1160a,1160 b grips the element flange 506,606, by pressing the hook's mouth,against the edge of the element flange 506,606 with enough force toovercome the bias of the hook flange's extent toward the base, until theflange 506,606 is seated in the hook's enclosure. The attachment bore1152 a,1152 b of the clip 1150 a,1150 b is positioned on the clip 1150a,1150 b such that when the clip 1150 a,1150 b is properly applied tothe flange 506,606, the attachment bore 1152 a,1152 b is aligned withthe mounting screw hole 509,609 on the flange 506,606 (see FIGS. 12b-h). Further, the posterior opening of the attachment bore 1152 a,1152b is preferably surrounded by a clip retaining features (e.g., a raisedwall 1162 a,1162 b), the outer diameter of which is dimensioned suchthat the raised wall 1162 a,1162 b fits into the mounting screw hole509,609 on the element flange 506,606. Thus, when the clip 1150 a,1150 bis so applied to the element flange 506,606, the element flange 506,606will be received into the hook's enclosure against the spring bias ofthe hook's extent, until the attachment bore 1152 a,1152 b is alignedwith the mounting screw hole 509,609, at which time the raised wall 1162a,1162 b will snap into the mounting screw hole 509,609 under the forceof the hook's extent's spring bias. This fitting prevents the clip 1150a,1150 b from slipping off the flange 506,606 under stresses in situ.Each of the laterally extending flanges 1156 a,1156 b and 1158 a,1158 bof the clip 1150 a,1150 b is sized to cover at least a portion of arespective one of the bone screw heads when the clip 1150 a,1150 b isattached in this manner to the flange 506,606 (see FIGS. 12 b-h), sothat, e.g., the clips 1150 a,1150 b help prevent the bone screws frombacking out.

Referring again to FIGS. 11 a-e, the clip applicator 1100 has a pair oftongs 1102 a,1102 b hinged at a proximal end 1104 of the clip applicator1100. Each tong 1102 a,1102 b has an attachment feature (e.g., a nub1108 a,1108 b) at a distal end 1106 a,1106 b. Each nub 1108 a,1108 b isdimensioned such that it can be manually friction locked into either ofthe attachment bores 1152 a,1152 b of the retaining clips 1150 a,1150 b.Thus, both clips 1150 a,1150 b can be attached to the clip applicator1100, one to each tong 1102 a,1102 b (see FIGS. 11 d and 11 e).Preferably, as shown in FIGS. 11 d and 11 e, the clips 1150 a,1150 b areattached so that their hook flanges 1154 a,1154 b are directed towardone another, so that they are optimally situated for attachment to theelement flanges 506,606 of the cervical disc replacement device 400 (seeFIG. 12 a).

Preferably, the clips 1150 a,1150 b are attached to the clip applicator1100 as described above prior to delivery to the surgeon. The assemblyis preferably provided sterile to the surgeon in a blister pack.Accordingly, when the surgeon is ready to mount the clips 1150 a,1150 bto the element flanges 506,606 of the cervical disc replacement device400, the surgeon opens the blister pack and inserts the tongs 1102a,1102 b of the clip applicator 1100 (with the clips 1150 a,1150 battached) into the treatment area.

Accordingly, and referring again to FIGS. 12 a-h, the clips 1150 a,1150b can be simultaneously clipped to the upper 500 and lower 600 elements'flanges 506,606 (one to each flange 506,606) using the clip applicator1100. More particularly, the mouths of the clips 1150 a,1150 b can bebrought to bear each on a respective one of the flanges 506,606 bymanually squeezing the tongs 1102 a,1102 b (having the clips 1150 a,1150b attached each to a set of the distal ends of the tongs 1102 a,1102 b)toward one another when the mouths of the clips 1150 a,1150 b aresuitably aligned with the flanges 506,606 (see FIG. 12 a). Once theclips 1150 a,1150 b have been attached to the flanges 506,660 with theraised walls 1162 a,1162 b fitting into the mounting screw holes 509,609of the flanges 506,606, the clip applicator 1100 can be removed from theclips 1150 a,1150 b by manually pulling the nubs 1108 a,1108 b out ofthe attachment bores 1152 a,1152 b, and the clip applicator 1100 can beremoved from the treatment area.

Turning to FIGS. 19 a and b, an alternate retaining device to retainingclips 1150 aand b, is shown. The surgeon can secure the bone screwsthrough use of retaining devices 1900 a,1900 b comprising threadedmembers 1910 a,1910 b and head flanges 1920 a,1920 b extendingtherefrom. As is seen in the figures, mounting screw holes 509,609 arethreaded for use with mounting screws 714 a,714 b. This same threadedconfiguration is useable with threaded members 1910 a,1910 b. Inparticular, once the mounting screws 714 a,714 b and the insertion plate700 are removed, the surgeon applies retaining devices 1900 a,1900 b byinserting and rotating threaded members 1910 a,1910 b into mountingscrew holes 509,609. Upon tightening of retaining devices 1900 a,1900 bin this manner, rim portions 1930 a,1930 b thereof cover at least aportion of a respective one of the bone screw heads so that the bonescrews are prevented from backing out of bone screw holes 508 a,508b,608 a,608 b. Preferably, each of the head flanges 1920 a,1920 b has athickness dimension 1940 a,1940 b and/or a configuration of stressrelief areas 1960 a,1960 b (or other suitable feature), such as in aconvex construction 1950 a,1950 b as viewed from the perspective of thethreaded member 1910 a,1910 b, that allows it to flex toward a flatterstate (stated alternatively, bending backward) as the threaded member1910 a,1910 b is advanced into the mounting screw hole 509,609 underforce, and this flexing stresses the threaded member 1910 a,1910 b toexpand or exert pressure upon its threaded connection within theassociated mounting screw hole 509,609, thus preventing backout of thethreaded member 1910 a,1910 b from the mounting screw hole 509,609. Inthis manner, the retaining devices 1900 a,1900 b not only preventbackout of the bones screws from the bone screw holes 508 a,508 b,608a,608 b, but also prevent backout of the threaded member 1910 a,1910 bfrom the mounting screw holes 509,609.

After implanting the cervical disc replacement device 400 as described,the surgeon follows accepted procedure for closing the treatment area.

Referring now to FIGS. 14 a-e, an alternate dual cervical discreplacement device configuration and alternate insertion plates for usetherewith, suitable, for example, for implantation in two adjacentcervical intervertebral spaces, are illustrated in exploded perspective(FIG. 14 a), anterior (FIG. 14 b), posterior (FIG. 14 c), lateral (FIG.14 d), and collapsed perspective (FIG. 14 e) views. Referring now alsoto FIGS. 15 a-c, an alternate upper element of the configuration isshown in posterior (FIG. 15 a), anterior (FIG. 15 b), and antero-lateral(FIG. 15 c) views. Referring now also to FIGS. 16 a-c, an alternatelower element of the configuration is shown in posterior (FIG. 16 a),anterior (FIG. 16 b), and antero-lateral (FIG. 16 c) views. Referringnow also to FIGS. 17 a-c, an alternate, upper, insertion plate of theconfiguration is shown in anterior (FIG. 17 a), posterior (FIG. 17 b),and antero-lateral (FIG. 17 c) views. Referring now also to FIGS. 18a-c, an alternate, lower, insertion plate of the configuration is shownin anterior (FIG. 18 a), posterior (FIG. 18 b), and antero-lateral (FIG.18 c) views.

More particularly, the alternate dual cervical disc replacement deviceconfiguration 1350 is suitable, for example, for implantation into twoadjacent cervical intervertebral spaces. The configuration preferably,as shown, includes an alternate, upper, cervical disc replacement device1400 (including an upper element 1500 and an alternate, lower, element1600), for implantation into an upper cervical intervertebral space, andfurther includes an alternate, lower, cervical disc replacement device2400 (including an alternate, upper, element 2500 and a lower element2600), for implantation into an adjacent, lower, cervical intervertebralspace. The illustrated alternate, upper, embodiment of the cervical discreplacement device is identical in structure to the cervical discreplacement device 400 described above (and thus like components arelike numbered, but in the 1400s rather than the 400s, in the 1500 srather than the 500s, and in the 1600s rather than the 600s), with theexception that the flange 1606 of the lower element 1600 is configureddifferently and without bone screw holes. The illustrated alternate,lower, embodiment of the cervical disc replacement device is identicalin structure to the cervical disc replacement device 400 described above(and thus like components are like numbered, but in the 2400s ratherthan the 400s, in the 2500s rather than the 500s, and in the 2600srather than the 600s), with the exception that the flange 2506 of theupper element 2500 is configured differently and without bone screwholes.

More particularly, in the alternate, upper, cervical disc replacementdevice 1400 of this alternate configuration, the flange 1606 of thelower element 1600 does not have bone screw holes, but has at least onemounting feature (e.g., a mounting screw hole) 1609 for attaching thelower element 1600 to the alternate, upper, insertion plate 1700(described below). Similarly, and more particularly, in the alternate,lower, cervical disc replacement device 2400 of this alternateconfiguration, the flange 2506 of the upper element 2500 does not havebone screw holes, but has at least one mounting feature (e.g., amounting screw hole) 2509 for attaching the upper element 2500 to thealternate, lower, insertion plate 2700 (described below). As can be seenparticularly in FIGS. 14 a-c, 15 b, 16 b, 17 a, and 18 a, the extent ofthe flange 1606 is laterally offset to the right (in an anterior view)from the midline (and preferably limited to support only the mountingscrew hole 1609), and the extent of the flange 2506 is laterally offsetto the left (in an anterior view) from the midline (and preferablylimited to support only the mounting screw hole 2509), so that theflanges 1606,2506 avoid one another when the alternate lower element1600 of the alternate, upper, cervical disc replacement device 1400, andthe alternate upper element 2500 of the alternate, lower, cervical discreplacement device 2400, are implanted in this alternate configuration(FIGS. 14 a-e).

It should be noted that the alternate, upper, cervical disc replacementdevice 1400 does not require both elements 1500,1600 to be secured to avertebral body. Only one need be secured to a vertebral body, becausedue to natural compression in the spine pressing the elements' bearingsurfaces together, and the curvatures of the saddle-shaped bearingsurfaces preventing lateral, anterior, or posterior movement relative toone another when they are compressed against one another, if one element(e.g., the upper element 1500) is secured to a vertebral body (e.g., tothe upper vertebral body by bone screws through the bone screw holes1508 a,1508 b of the element flange 1506), the other element (e.g., thealternate, lower, element 1600) cannot slip out of the intervertebralspace, even if that other element is not secured to a vertebral body(e.g., to the middle vertebral body). Similarly, the alternate, lower,cervical disc replacement device 2400 does not require both elements2500,2600 to be secured to a vertebral body. Only one need be secured toa vertebral body, because due to natural compression in the spinepressing the elements' bearing surfaces together, and the curvatures ofthe saddle-shaped bearing surfaces preventing lateral, anterior, orposterior movement relative to one another when they are compressedagainst one another, if one element (e.g., the lower element 2600) issecured to a vertebral body (e.g., to the lower vertebral body by bonescrews through the bone screw holes 2608 a,2608 b of the element flange2606), the other element (e.g., the alternate, upper, element 2500)cannot slip out of the intervertebral space, even if that other elementis not secured to a vertebral body (e.g., to the middle vertebral body).

Accordingly, the alternate, upper, insertion plate 1700 is provided tofacilitate a preferred simultaneous implantation of the upper and lowerelements 1500,1600 of the alternate, upper, cervical disc replacementdevice 1400 into the upper intervertebral space. Similarly, thealternate, lower, insertion plate 2700 is provided to facilitate apreferred simultaneous implantation of the upper and lower elements2500,2600 of the alternate, lower, cervical disc replacement device 2400into the lower intervertebral space. The upper and lower elements1500,1600 are held by the insertion plate 1700 (preferably usingmounting screws 1714 a,1714 b) in a preferred relationship to oneanother that is suitable for implantation, identical to the preferredrelationship in which the upper and lower elements 500,600 are held bythe insertion plate 700 as described above. Similarly, the upper andlower elements 2500,2600 are held by the insertion plate 2700(preferably using mounting screws 2714 a,2714 b) in a preferredrelationship to one another that is suitable for implantation, identicalto the preferred relationship in which the upper and lower elements500,600 are held by the insertion plate 700 as described above.

The illustrated alternate, upper, insertion plate 1700 is identical instructure to the insertion plate 700 described above (and thus likecomponents are like numbered, but in the 1700s rather than the 700s),with the exception that the lower flange 1704 b is offset from themidline (to the right in an anterior view) to align its mounting screwhole 1712 b with the offset mounting screw hole 1609 of the alternatelower element 1600 of the alternate, upper, cervical disc replacementdevice 1400. Similarly, the illustrated alternate, lower, insertionplate 2700 is identical in structure to the insertion plate 700described above (and thus like components are like numbered, but in the2700s rather than the 700s), with the exception that the upper flange2704 a is offset from the midline (to the left in an anterior view) toalign its mounting screw hole 2712 a with the offset mounting screw hole2509 of the alternate upper element 2500 of the alternate, lower,cervical disc replacement device 2400.

Accordingly, the upper and lower elements 1500,1600, being held by theinsertion plate 1700, as well as the upper and lower elements 2500,2600,being held by the insertion plate 2700, can be implanted using theinsertion handle 800, insertion pusher 900, drill guide 1000, clips 1150a,1150 b (one on the upper element flange 1506, and one on the lowerelement flange 2606, because only the upper element 1500 and the lowerelement 2600 are secured by bone screws), and clip applicator 1100, inthe manner described above with respect to the implantation of thecervical disc replacement device 400.

It should be noted that the described alternate configuration (thatincludes two cervical disc replacement devices) presents the cervicaldisc replacement devices to the surgeon in a familiar manner. That is,by way of explanation, current cervical fusion surgery involves placinga fusion device (e.g., bone or a porous cage) in between the upper andmiddle cervical intervertebral bones, and in between the middle andlower vertebral bones, and attaching an elongated two-level cervicalfusion plate to the anterior aspects of the bones. Widely used two-levelcervical fusion devices (an example two level fusion plate 1350 is shownin anterior view in FIG. 13 c and in lateral view in FIG. 13 d) areconfigured with a pair of laterally spaced bone screw holes 1352 a,1352b on an upper end 1354 of the plate 1350, a pair of laterally spacedbone screw holes 1356 a,1356 b on a lower end 1358 of the plate 1350,and a pair of laterally spaced bone screw holes 1360 a,1360 b midwaybetween the upper and lower ends 1354,1358. To attach the plate 1350 tothe bones, bone screws are disposed through the bone screw holes andinto the corresponding bones. This prevents the bones from movingrelative to one another, and allows the bones to fuse to one anotherwith the aid of the fusion device.

Accordingly, as can be seen in FIG. 14 b, when the upper and lowerelements 1500,1600 of the cervical disc replacement device 1400, and theupper and lower elements 2500,2600 of the cervical disc replacementdevice 2400, are held in the preferred spatial relationship and alignedfor implantation, the upper element flange 1506 and lower element flange2606, and their bone screw holes 1508 a,1508 b and 2608 a,2608 b,present to the surgeon a cervical hardware and bone screw holeconfiguration similar to a familiar two level cervical fusion plateconfiguration (as described above, a middle pair of bone screws holes isnot needed; however, middle bone screw holes are contemplated by thepresent invention for some embodiments, if necessary or desirable). Themounting of the elements 1500,1600 to the insertion plate 1700 allowsthe elements 1500,1600 to be manipulated as a single unit forimplantation (by manipulating the insertion plate 1700), similar to theway a cervical fusion plate is manipulatable as a single unit forattachment to the bones. Similarly, the mounting of the elements2500,2600 to the insertion plate 2700 allows the elements 2500,2600 tobe manipulated as a single unit for implantation (by manipulating theinsertion plate 2700), similar to the way a cervical fusion plate ismanipulatable as a single unit for attachment to the bones. This aspectof the present invention simplifies and streamlines the cervical discreplacement device implantation procedure.

While there has been described and illustrated specific embodiments ofcervical disc replacement devices and insertion instrumentation, it willbe apparent to those skilled in the art that variations andmodifications are possible without deviating from the broad spirit andprinciple of the invention. The invention, therefore, shall not belimited to the specific embodiments discussed herein.

1. For an intervertebral disc replacement device having a flange and atleast one bone screw hole for receipt therethrough of at least one bonescrew and at least one mounting hole, a retaining device for said atleast one bone screw, comprising: a threaded attachment member forthreaded engagement with said at least one mounting hole in said flangeof said intervertebral disc replacement device; and a head flangedefined by an outer perimeter, said head flange extending from saidthreaded attachment member, wherein said head flange is in partabuttingly received against a side of said flange of said intervertebraldisc replacement device and said outer perimeter is partially receivedover a portion of said at least one bone screw to prevent said at leastone bone screw from backing out of said at least one bone screw holewhen said retaining device is fully engaged with said intervertebraldisc replacement device, wherein said head flange includes a solidportion and at least one stress relief area wholly contained within theconfines of and not extending through said outer perimeter so that theat least one stress relief area is bounded on all lateral sides by thesolid portion, the at least one stress relief located on said headflange at a point other than a central point of said head flange andproviding for said head flange to be at least somewhat flexible in asubstantially axial direction of said threaded attachment member.
 2. Aretaining device as recited in claim 1, wherein said head flange is of aconvex construction from an orientation taken in relation to saidthreaded attachment member.
 3. A retaining device as recited in claim 2,said head flange flexing in such a manner so as to cause said convexconstruction thereof to become flatter when said retaining device isfully engaged with said intervertebral disc replacement device, whereinsaid flatter condition of said head flange causes said threadedattachment member to exert pressure along its said threaded engagementwith said at least one mounting hole so as to prevent said threadedattachment member from backing out of said at least one mounting hole.4. A retaining device as recited in claim 3, said at least one bonescrew hole comprising first and second bone screw holes and said atleast one bone screw comprising first and second bone screws.
 5. Aretaining device as recited in claim 4, wherein said outer perimeter ispartially received over portions of said first and second bone screws toprevent said first and second bone screws from backing out of said firstand second bone screw holes, respectively, when said retaining device isfully engaged with said intervertebral disc replacement device.
 6. Aretaining device as recited in claim 1, wherein the at least one stressrelief area is circular.
 7. A retaining device as recited in claim 1,wherein said head flange includes two stress relief areas.
 8. Aretaining device as recited in claim 1, wherein said head flangeincludes three stress relief areas.
 9. A retaining device as recited inclaim 1, wherein said head flange includes four stress relief areas. 10.A retaining device as recited in claim 9, wherein the stress reliefareas are circular.
 11. For an intervertebral disc replacement devicehaving a flange and at least one bone screw hole for receipttherethrough of at least one bone screw and at least one mounting hole,a retaining device for said at least one bone screw, comprising: athreaded attachment member for threaded engagement with said at leastone mounting hole in said flange of said intervertebral disc replacementdevice; and a head flange defined by an outer perimeter, said headflange extending from said threaded attachment member, wherein said headflange is in part abuttingly received against a side of said flange ofsaid intervertebral disc replacement device and said outer perimeter ispartially received over a portion of said at least one bone screw toprevent said at least one bone screw from backing out of said at leastone bone screw hole when said retaining device is fully engaged withsaid intervertebral disc replacement device, wherein said head flangeincludes a solid portion and at least one circular stress relief areawholly contained within the confines of and not extending through saidouter perimeter so that the at least one stress relief area iscompletely surrounded by the solid portion, the at least one stressrelief located on said head flange at a point other than a central pointof said head flange and providing for said head flange to be at leastsomewhat flexible in a substantially axial direction of said threadedattachment member.
 12. A retaining device as recited in claim 11,wherein said head flange is of a convex construction from an orientationtaken in relation to said threaded attachment member, said head flangeflexing in such a manner so as to cause said convex construction thereofto become flatter when said retaining device is fully engaged with saidintervertebral disc replacement device, wherein said flatter conditionof said head flange causes said threaded attachment member to exertpressure along its said threaded engagement with said at least onemounting hole so as to prevent said threaded attachment member frombacking out of said at least one mounting hole.
 13. A retaining deviceas recited in claim 12, wherein said head flange includes four circularstress relief areas.
 14. For an intervertebral disc replacement devicehaving a flange and at least one bone screw hole for receipttherethrough of at least one bone screw and at least one mounting hole,a retaining device for said at least one bone screw, comprising: athreaded attachment member for threaded engagement with said at leastone mounting hole in said flange of said intervertebral disc replacementdevice; and a head flange defined by an outer perimeter, said headflange extending from said threaded attachment member and being of aconvex construction from an orientation taken in relation to saidthreaded attachment member, wherein said head flange is in partabuttingly received against a side of said flange of said intervertebraldisc replacement device and said outer perimeter is partially receivedover a portion of said at least one bone screw to prevent said at leastone bone screw from backing out of said at least one bone screw holewhen said retaining device is fully engaged with said intervertebraldisc replacement device, wherein said head flange includes a solidportion and four circular stress relief areas wholly contained withinthe confines of and not extending through said outer perimeter so thatthe four stress relief areas are bounded on all lateral sides by thesolid portion, the four stress relief areas located on said head flangeat a point other than a central point of said head flange and providingfor said head flange to be at least somewhat flexible in a substantiallyaxial direction of said threaded attachment member, said head flangeflexing in such a manner so as to cause said convex construction thereofto become flatter when said retaining device is fully engaged with saidintervertebral disc replacement device, wherein said flatter conditionof said head flange causes said threaded attachment member to exertpressure along its said threaded engagement with said at least onemounting hole so as to prevent said threaded attachment member frombacking out of said at least one mounting hole.
 15. A retaining deviceas recited in claim 14, wherein said at least one bone screw holecomprising first and second bone screw holes and said at least one bonescrew comprising first and second bone screws.
 16. A retaining device asrecited in claim 15, wherein said outer perimeter is partially receivedover portions of said first and second bone screws to prevent said firstand second bone screws from backing out of said first and second bonescrew holes, respectively, when said retaining device is fully engagedwith said intervertebral disc replacement device.